1. Field of the Invention
This invention relates to tool holder assemblies and, more particularly, to a tool holder assembly having means to lock the clamping nut in clamped position on the socket member.
2. Prior Art
Tool utilizing devices, particularly machine tools, having tool spindles frequently employ quick change chucks or tool holders in which the tool can be quickly inserted and released. In a known format for such tool holders a spindle attached socket member is provided with a cylindrical end portion having a tapered socket opened to the end. The cylindrical portion has external threads and a nut assembly is received over the cylindrical end and engaged with the external threads. A tool adapter is provided in which the tool is secured projecting from an end of the adapter. Mating projections and recesses on the tool adapter, socket member and nut cooperate to allow the tool adapter to be quickly inserted in the socket, clamped therein, unclamped therefrom and removed from the socket. Various combinations of clamping means have been known to the art and include, for example, radial projections on the tool adapter alignable with radial slots in an inturned end flange of the nut and slots in the peripheral wall of the socket member and the reverse thereof, i.e. flats on a projecting flange on the tool adapter alignable with radially inwardly projecting clamping lugs on the nut and keys carried by the inner diameter of the peripheral wall of the socket member. In the first instance, the nut is movable from a position where the nut slots are aligned with the socket member slots and the nut flange is spaced from the end of the socket, to allow insertion of the tool adapter, to a clamped position at which the nut slots are rotated with respect to the tool adapter radial projections, now received snuggly in the socket member slots and where the nut flange is axially moved towards the socket to engage the underside of the tool adapter projections. In the latter embodiment, the nut is rotatable from a position where the nut clamping lugs are aligned with the keys of the socket member, at which position the flats of the tool adapter allow insertion past the clamping lugs into engagement with the keys, the nut then being rotatable to a clamping position where the lugs are circumferentially displaced from the keys and engage the underside of the tool adapter flange to seat it in the socket. Other variations are also known where the clamping is done by an independent member carried by and rotatable with respect to the nut, etc. Such devices are shown, for example, in U.S. Pat. Nos. 2,719,722; 3,663,028; 3,730,540; and 4,298,208.
In a common variant of such prior systems, spring means are used to urge the nut from the unclamped position to the clamped position with abutment and lock means provided to maintain the nut, against the spring, in the unclamped tool insertion and removal position. The nut threads are generally chosen to be of a hand such that when the spindle is rotating in its primary tool using direction the nut will tend to tighten on the spindle to maintain proper clamping force.
Although such prior art tool holder assemblies have achieved widespread success, recent developments in machine tools, such as, for example, high speed tooling, increased machine tool feed rates, emergency braking, and bi-directional spindle rotation, can lead to problems particularly where the spring force of the automatic locknut in conjunction with mechanical energy stored by the elastic deformation and frictional resistances of the nut threads with or without spring actuating means is not adequate to maintain a desired clamping force. Clamping force may also be lost because of unbalanced dynamic forces and also through vibrations produced by the machine tool operations and from reverse rotation, and also from instantaneous braking.